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Full text of "Text Book Of Mechanical Engineering"

1186                          Appendix  VL

where it is kept at such level as to just ooze at nipple F, its outlet
being further regulated by handscrew G. A wooden float H dips
in mercury in chamber D, and carries by a vertical rod, the piston
valve j controlling the admission of extra or adjusting air. A
pipe R connects the second nipple K with the opening L just over
the wooden float; and the tubular valve M, operated from a
governor, acts as a throttle on the prepared mixture on its way to
the engine. When the carburettor is in action, the petrol is
drawn from Q to P past the spray nipple by air entering through
f                           gauze gratings; but if the suction be excessive, a partial vacuum

|                           is produced immediately over the float H by means of the suction

?                           pipe KRL, and the piston valve j automatically admits the larger

f                           amount of extra air to adjust the greater vaporisation of petrol, a

I                           mixture of constant richness resulting.    The mercury is steadied

r'}                            by steel balls, and kept from oxidation by a film of glycerine.

?                                Electric ignition is the only method  now employed.     In

I                           addition to the examples at p. 963, two other varieties are given

g                           in Figs.   1043  and   1044, where  the firing, arranged for four

||                           cylinders, can be easily applied to any multiple-cylinder engine.

Fig. 1044 shews the ordinary accumulator system, where  the
:?                           primary wire n b from the accumulators a is connected in series

<j j|                          with the induction coil e and interrupting cam cy the former having

a trembling hammer, and the latter a baseboard d for angular
adjustment. The distributor g lies in the secondary circuit m
which is connected at r to the firing plugs , returning by earth
(engine frame) at /, and the choice of fire is decided by the wiper
I 1                          in contact at h. Both cam and distributor are rotated by chains

.                  at equal speed with the valve shaft/ and four times in a revolu-

tion (depending on number of cylinders) cam c breaks the firing
circuit, and a highly intensified current-is induced, which sparks
at the plugs kk in one cylinder after another; the usual order of
cylinders being i, 3, 2, 4, thus taking opposite cranks in pairs,
The wiper baseboard g and trip board d can both be simulta-
neously turned through a small angle, as shewn at dl gl, by the
lever #, in order to advance the spark, that is, cause it to occur
earlier in die compression stroke, a useful method of hand
governing within considerable limits. The switch / puts the
apparatus ia or out of gear when required,

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